Algae have several industrial applications that can lower the cost of biofuel co-production. Among these co-production applications, environmental and wastewater bioremediation are increasingly ...important. Heavy metal pollution and its implications for public health and the environment have led to increased interest in developing environmental biotechnology approaches. We review the potential for algal biosorption and/or neutralization of the toxic effects of heavy metal ions, primarily focusing on their cellular structure, pretreatment, modification, as well as potential application of genetic engineering in biosorption performance. We evaluate pretreatment, immobilization, and factors affecting biosorption capacity, such as initial metal ion concentration, biomass concentration, initial pH, time, temperature, and interference of multi metal ions and introduce molecular tools to develop engineered algal strains with higher biosorption capacity and selectivity. We conclude that consideration of these parameters can lead to the development of low-cost micro and macroalgae cultivation with high bioremediation potential.
•Algae biomass, after lipid extraction and biofuel production, has the potential for biosorption and/or neutralization of the toxic effects of heavy metal ions from industrial wastewaters.•The pretreatment, immobilization, and factors affecting biosorption capacity, such as initial metal ion concentration, biomass concentration, initial pH, time, temperature, and interference of anions and cations are important parameters to be considered.•These parameters can lead to the development of low-cost microalgae cultivation with high bioremediation potential.•These applications make algae a suitable candidate for wastewaters bioremediation/biorefinery.
Despite attracting many attentions in the past decades, microalgal cultivation still faces many challenges for industrialisation. Growth, as one of the most crucial characteristics of a microalgal ...cultivation system, has been a significant subject for modelling. This paper presents a review of available models in the literature regarding the effect of process parameters such as light, temperature, nutrients, oxygen accumulation, salinity, and pH and carbon, on the growth rate of microalgal cells to understand their application in large-scale microalgal production. The existing models are classified based on the process conditions or parameters they considered in the formulation, and where multiple parameters were included the model was broken into separate functions, and each function was presented in the associated section. The most prominent result of this review is the huge gap between models and their validity for outdoor systems. It seems that to find suitable models for a real condition application, a new pathway is needed where models are developed based on the behaviour of the outdoor cultures in long-term. There are some effects such as adaptation which are difficult to model in short-term modelling while if the long-term approach is used these effects can be considered negligible. These characteristics of outdoor cultivation help in simplification of the models and less struggle in their validation. Moreover, using saline water is an effective way to improve the viability of algal production which requires understanding the relationship between growth and salinity of the medium. Such models are missing in the literature.
•Most models are not validated for outdoor systems.•Models are designed only for short-term prediction but not long-term.•Salinity is a key factor for growth but is neglected in the modelling studies.•There is lack of comprehensive model combining the effect of all major factors.
Microalgae have gained increased attention as a viable, eco-friendly and alternative source of green bioenergy. To compete in the fuel market, saline microalgae cultivation for biofuel production ...would need to be economically sustainable and co-cultivation of saline microalgae using only saline water and recycled nutrient can potentially be the best solution to reduce the excessive use and prompt downsizing of natural resources like fresh water and fertilizers. This review provides a critical analysis on the selection of potential biofuel producing marine, halotolerant and halophilic microalgae. Here we proposed a microalgae co-cultivation strategy from seawater salinity (35ppt) to salt saturation (300ppt) with biofuel as the main output. We focused that adaptation of a co-cultivation strategy could reduce 95%, 74% and 51% of the overall nutrient waste compared to the monoculture of marine, halotolerant and halophilic microalgae. This paper also highlights a cultivation strategy using both mono and mixed culture over the period of increased saline condition and compares mass industrial-scale biofuel production from microalgae in three sites in Western Australia.
The successful cultivation of microalgae in wastewater establishes a waste to profit scenario as it combines treatment of a waste stream with production of valuable end-products. Here, growth and ...nutrient removal efficiency of three different locally isolated microalgal cultures (Chlorella sp., Scenedesmus sp., and a mixed consortium) cultivated in anaerobically digested municipal centrate (ADMC) and anaerobically digested abattoir effluent (ADAE) was evaluated. No significant differences (P > 0.05) in specific growth rate and biomass productivity were recorded between Chlorella monocultures and the mixed culture grown in both effluents. Scenedesmus sp. monocultures was found incapable of growth in both ADMC and ADAE throughout the cultivation period resulting in the collapse of cultures and no further measurements on the growth, biomass production and nutrient removal efficiency of this alga in both effluent. Fq´/Fm´ values which represent the immediate photo-physiological status of microalgae found to be negatively inhibited when Scenedesmus sp. was grown in both effluents throughout the cultivation period. Fq´/Fm´ values of Chlorella sp. monocultures and the mixed cultures recovered back to normal (≈0.6) after an initial drop. Ammonium removal rates was found to be significantly higher (≈2 folds) for Chlorella sp. monocultures grown in both ADMC and ADAE when compared to the mixed cultures. Nonetheless, no significant differences were observed in the removal of phosphate for both cultures in the different effluents. The total protein and carbohydrate content of the biomass produced was similar for both microalgae cultures grown using ADAE and ADMC. However, chlorophyll a and total carotenoids content were found to be higher (P < 0.05) for the cultures grown in ADAE than ADMC. Overall, Chlorella sp. monoculture was the most efficient option for treating both ADMC and ADAE while simultaneously generating protein rich biomass (up to 49%) that can be potentially exploited as aquaculture feedstock.
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•Microalgae growth in two raw undiluted anaerobic digestates were achieved.•Biomass productivity of mono Chlorella and mixed cultures were similar.•Scenedesmus sp. did not grow in both undiluted anaerobic digestates.•Up to 95% (NH3-N) and 58% (PO43−) removal rates were achieved.•Protein content of up to 49% were achieved for wastewater grown algae.
Sufficient and reliable long-term field data on the growth, productivity and nutrient removal rates of microalgal based wastewater treatment system is essential to validate its overall ...techno-economic feasibility. Here, we investigated the semi-continuous microalgal cultivation of Scenedesmus sp. in anaerobically digested abattoir effluent (ADAE) for 13 months in outdoor raceway ponds operated at 20 cm depth. This study was initiated with three different cultures consisting of 1) monocultures of Chlorella sp., 2) Scenedesmus sp., and 3) an equal mixed concentration of both microalgae species. However, after 15 weeks, Scenedesmus sp. was found to be the most dominant microalgae species in all the different cultures, even completely taking over the Chlorella sp. monoculture. Over the course of summer and early autumn, the average weekly biomass productivity of Scenedesmus sp. cultures was 12.5 ± 0.6 g m−2 d−1 which was 16% and 30% higher than productivities recorded in spring and winter, respectively. All available ammoniacal nitrogen (NH3–N) was found to be exhausted during each growth period with an average 33.6% nitrogen assimilation rate. The average rate of phosphate and COD (chemical oxygen demand) removals were 85.2% and 37.5% throughout the cultivation period. No significant differences were found in carbohydrate, lipid and protein content of Scenedesmus sp. during different seasons of the year. Over 53% increase in biomass productivity can be achieved if CO2 is added to control culture pH at pH 6.5. Here, we successfully demonstrated reliability of continuous long-term cultivation of microalgae in ADAE for simultaneous wastewater treatment and algal biomass production.
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•Scenedesmus sp. cultivated in waste effluent for 13 months in outdoor raceway ponds.•Scenedesmus sp. was the most dominant species in cultures taking over Chlorella sp.•Biomass productivity was 12.5 ± 0.6 g m−2 d−1 in summer which was 30% higher than winter.•All ammoniacal nitrogen and 85% of phosphorus were removed from the system.•34 and 26% nitrogen and phosphorus fixed into biomass during entire cultivation period.
A model based framework was established for large scale assessment of microalgae production using anaerobically digested effluent considering varied climatic parameters such as solar irradiance and ...air temperature. The aim of this research was to identify the optimum monthly average culture depth operation to minimize the cost of producing microalgae grown on anaerobic digestion effluents rich in ammoniacal nitrogen with concentration of 248 mg L−1. First, a productivity model combined with a thermal model was developed to simulate microalgae productivity in open raceway ponds as a function of climatic variables. Second, by combining the comprehensive open pond model with other harvesting equipment, the final techno economic model was developed to produce a microalgae product with 20 wt% biomass content and treated water with <1 mg L−1 ammoniacal nitrogen. The optimization approach on culture depth for outdoor open raceway ponds managed to reduce the cost of microalgae production grown in anaerobic digested wastewater up to 16 %, being a suitable solution for the production of low cost microalgae (1.7 AUD kg−1 dry weight) at possible scale of 1300 t dry weight microalgae yr−1.
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•Minimum microalgae production cost can reach <2 AUD kg−1 using AD effluent.•Culture depth optimization can reduce the cost of microalgae production 16 %.•At optimum operation, it is possible to produce 2.7 kg biomass from AD effluent.
Anaerobic digestate of food waste as a waste product of anaerobic digestion contains a significant amount of nutrients making its direct disposal prohibitive due to environmental regulations. ...However, the nutrients in this waste are a valuable feedstock for waste-to-product endeavours such as microalgae cultivation coupled to the treatment of the digestate. A limitation to this path is the high toxic concentration of ammonia nitrogen in the digestate which limits microalgae growth, leading to the requirement for significant dilution before use. This study focused on the bioprospecting and sourcing of species capable of sustained growth in very high concentrations of ammonia nitrogen. Ten local strains of microalgae were isolated, comprising mainly of unicellular species, a colonial species, and a filamentous species. Three unicellular species were chosen (
Chlorella
sp., MUR 271;
Scenedesmus obliquus
(
Tetradesmus obliquus
), MUR 272; and
Oocystis
sp., MUR 273) and screened alongside previously isolated strains (
Scenedesmus quadricauda,
MUR 268;
Chlorella
sp., MUR 269; and
Scenedesmus dimorphus
(
Tetradesmus dimorphus
) MUR 270) which had undergone long-term acclimation in digestate. The most tolerant of the newly isolated strains was MUR 273 (
Oocystis
sp.), capable of proliferation in up to 600 mg L
−1
NH
3
-N concentration in digestate. The maximum specific growth rate,
μ
max
, of MUR 273 was 0.36 ± 0.01 day
−1
at 150 mg L
−1
NH
3
-N. The results indicate that MUR 273 displayed tolerance levels similar to that obtained with MUR 268 which had previously undergone long-term acclimation in digestate and could potentially be used in the treatment and valorization of the anaerobic digestate of food waste with significantly less dilution.
Wastewater generated within agricultural sectors such as dairies, piggeries, poultry farms, and cattle meat processing plants is expected to reach 600 million m3 yr−1 globally. Currently, the ...wastewater produced by these industries are primarily treated by aerobic and anaerobic methods. However, the treated effluent maintains a significant concentration of nutrients, particularly nitrogen and phosphorus. On the other hand, the valorisation of conventional microalgae biomass into bioproducts with high market value still requires expensive processing pathways such as dewatering and extraction. Consequently, cultivating microalgae using agricultural effluents shows the potential as a future technology for producing value-added products and treated water with low nutrient content. This review explores the feasibility of growing microalgae on agricultural effluents and their ability to remove nutrients, specifically nitrogen and phosphorus. In addition to evaluating the market size and value of products from wastewater-grown microalgae, we also analysed their biochemical characteristics including protein, carbohydrate, lipid, and pigment content. Furthermore, we assessed the costs of both upstream and downstream processing of biomass to gain a comprehensive understanding of the economic potential of the process. The findings from this study are expected to facilitate further techno-economic and feasibility assessments by providing insights into optimized processing pathways and ultimately leading to the reduction of costs.
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•Possibility of full removal of nitrogen and phosphorus from agricultural wastewater.•Process integration of microalgae cultivation with agricultural wastewater.•High productivity for microalgae grown in nutrient rich agricultural wastewater.•Cultivating microalgae in agricultural wastewater offers low-cost production.•Converting microalgae to value-added products might result in profitability.
Microalgae have tremendous potential for producing liquid renewable fuel. Many methods for converting microalgae to biofuel have been proposed; however, an economical and energetically feasible route ...for algal fuel production is yet to be found. This paper presents a review on the comparison of the most promising conversion pathways of microalgae to liquid fuel: hydrothermal liquefaction (HTL), wet extraction and non-destructive extraction. The comparison is based on important assessment parameters of product quality and yield, nutrient recovery, GHG emissions, energy and the cost associated with the production of fuel from microalgae, in order to better understand the pros and cons of each method. It was found that the HTL pathway produces more oil than the wet extraction pathway; however, higher concentrations of unwanted components are present in the HTL oil produced. Less nutrients (N and P) can be recovered in HTL compared to wet extraction. HTL consumes more fossil energy and generates higher GHG emissions than wet extraction, while the production cost of fuel from HTL pathway is lower than wet extraction pathway. There is considerable uncertainty in the comparison of the energy consumption and economics of the HTL pathway and the wet extraction pathway due to different scenarios analysed in the assessment studies. To be able to appropriately compare methodologies, the conversion methods should be analysed from growth to upgradation of oil utilising sufficiently similar assumptions and scenarios. Based on the data in available literature, wet oil extraction is the more appropriate system for biofuel production than HTL. However, the potential of alternative extraction/conversion technologies, such as, non-destructive extraction, need to be further assessed.
Anaerobic digestion (AD) of food waste diverts organic waste from landfills, generates sustainable baseload energy, and potentially an ecotoxic ammonia-rich digestate that requires post-treatment. ...Successful application of algal-based technology to treating high-ammonia AD effluents can be achieved by freshwater dilution. However, dilution of high-strength effluents with freshwater is currently unsustainable. Here, the feasibility of growing
Chlorella
sp. on the effluent of food waste anaerobic digestate with high ammonia content under recycling of the treated effluent was investigated for nutrient management and biomass production. The performance of the
Chlorella
sp. cultivated in repeated batch with effluent recycling (BR) and without recycling (BNR) was compared with repeated fed-batch mode with recycling (FR) and without recycling (FNR). Maximum cell density (6.1 × 10
7
cells mL
−1
) corresponding to the highest chlorophyll
a
(23.3 ± 1.3 mg L
−1
) content was found in the FNR. Ammonia removal rates were not significantly different among all tested treatments. In all treatments, the analysis of the operating efficiency of PSII photochemistry (
F
q
′/
F
m
′) of the culture showed values > 0.5, indicating cells were not subjected to physiological stress. Harvested
Chlorella
biomass composition showed no variation in the contents of total protein, carbohydrate, and lipids. Turbidity increase in cultures with effluent recycling versus without recycling was negligible (5%), demonstrating the suitability of effluent recycling in the microalgae-based treatment of high-strength ammonia food waste digestate.
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